Allow settings navigation items with no route entry

[Pytal]

Summary

Some apps register navigation entries with extraneous empty routes e.g.

server/apps/user_status/appinfo/info.xml

Line 18 in e81cb6e

<route />

Instead of adding empty routes we can allow no routes at all

This adjusts the core logic to allow no route entries and updates the XML schemas to pass xmllint used in https://github.com/nextcloud/.github/blob/ff4a6f1eacb53e4d3b5721e57743eb64242178a7/workflow-templates/lint-info-xml.yml

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)

[Pytal]

/backport to stable25

[ChristophWurst]

👍🙂

[ChristophWurst]

nit: squash

[nickvergessen]

No, need visibility for 3 approving people and the author together with the failing CI

[Pytal]

/backport to stable25

[backportbot-nextcloud]

The backport to stable25 failed. Please do this backport manually.

Details

# Switch to the target branch and update it
git checkout stable25
git pull origin/stable25

# Create the new backport branch
git checkout -b fix/foo-stable25

# Cherry pick the change from the commit sha1 of the change against the default branch
# This might cause conflicts. Resolve them.
git cherry-pick abc123

# Push the cherry pick commit to the remote repository and open a pull request
git push origin fix/foo-stable25

More info at https://docs.nextcloud.com/server/latest/developer_manual/getting_started/development_process.html#manual-backport

#36529